1. Technical Field
The present invention relates to a crystal oscillator, and in particular, to an amplitude controlled crystal oscillator having a peak detector, to adapt to a wider dynamic frequency range and a wider crystal indicator range.
2. Related Art
The oscillator is a component critical to the performance of modern electronic devices. Digital timepieces, computers, cameras, televisions, mobile phones, tablet computers, communications devices and the like all use a crystal oscillator to generate a desired clock signal.
FIG. 1 illustrates a conventional crystal oscillator circuit. The oscillator circuit includes an inverting amplifier consisting of a PMOS transistor M2, a resistor R13 and an NMOS transistor M1 and a feedback network consisting of, for example, a quartz crystal, a capacitor Cp and a resistor Re. The feedback network outputs a feedback signal to an input end of the inverting amplifier, thereby forming a closed loop feedback system.
FIG. 2 illustrates an oscillator circuit having a peak detector. The oscillator circuit includes a peak detector, for comparing a peak of an output signal of an oscillator and a reference voltage. When the oscillator circuit starts, amplitude of the output signal of the oscillator is lower, the peak detector outputs a higher voltage signal, and the voltage signal conducts the transistor M12, and applies a greater bias current to the inverting amplifier through a current mirror circuit consisting of M11 and M3, to facilitate the work of the oscillator. When the oscillator circuit is more stable, the peak detector detects a higher oscillator output voltage signal, thereby applying a smaller bias current, so that the stabilized oscillator output voltage is maintained at a lower level. The circuit has advantages of quickly starting and avoiding excessive consumption of energy after stabilization. However, the circuit has disadvantages of large noise and large jitter.